The invention relates to piston pumps and motors and more particularly to the type which is generally referred to in the art as radial piston variable displacement pumps. Radial pumps are distinguished from axial piston pumps in that they position their pistons in a radial pattern in a rotating cylinder block, while in axial piston pumps the pistons reciprocate along axis which are parallel to the axis of rotation of the cylinder block. Radial piston pumps of various types have been in existence for many decades and the state of the art is very refined. The pump displacement is varied by moving the cam ring out of concentric positioning with the rotating cylinder block whereby the pistons and their respective slipper shoes which ride on the inside surface of the cam ring reciprocate as the cylinder block rotates. Some prior art pumps move the cam ring in a lineal path while others pivot the cam ring about a point outside of the ring with some type of actuating means. The pump of the present invention is in the latter category just mentioned, and is pivoted about a pin which passes through the ring itself. The means in the prior art for moving and positioning the cam ring are extensive, as exemplified in the following U.S. Pat. Nos.: 2,566,418; 2,969,022; 2,895,416; 4,526,154.